Pressure regulating valves including those which are actuated by proportional solenoids are well known and are used for generating a pressure output signal which is proportional to an actuating force which acts on the control spool of the pressure regulating valve.
In a known pressure regulating valve the control spool of said pressure regulating valve comprises end faces which are designed to act as pressure metering areas. Provisions are made that the secondary pressure which builts up in the operating chamber of the valve, i.e. the chamber connected with a load can act upon said metering area, so that the control spool is moved contrary to the actuating force which also acts on the control spool. Eventually a balance will be achieved between the actuating force and the force created by the secondary pressure. In this known pressure regulating valve the diameter of the control spool will determine the size of the pressure metering surfaces or areas. If it becomes necessary to change the range within which the pressure may be adjusted then for such a valve the entire control spool has to be replaced, i.e. the entire valve has to be exchanged. Another disadvantage of this known valve resides in the fact that in the chambers at both ends of the control spool (chambers which are formed when the proportional solenoid is mounted on the valve housing) the full secondary pressure is present.
Applicant's proportional) valve disclosed in applicant's publication RD No. 29126/3.83 discloses a pressure regulating valve which makes use of metering spools provided at both ends of the control spool. Solenoids are provided at opposite ends of the valve housing and the solenoid pins abut at the appropriate metering spools. Assuming that the control spool is actuated by a proportional solenoid at one end, then the metering spool at the other end will be supplied with the secondary pressure, i.e. the pressure in the operating chamber which means the chamber which is connected with a load. Even though only one half of the control spool is active in controlling the fluid flow, the other half will also have to be moved together with the first-mentioned half, a situation which can lead to increased friction.
Applicant's proportional valve disclosed in applicant's publication RD No. 29384 uses two control spool means. It is a disadvantage that the size of the diameter of the two control spool means determines the size of the pressure metering area. Further, also the fluid will flow in axial direction through the control spool means. This causes a severe limitation of the amount of fluid which can be handled. The present invention is directed to overcoming one or more of the problems of the prior art, specifically the prior art set forth above.